1. Field of Invention
The present invention relates to a high-pressure mercury discharge lamp, which contains an ionizable filling including at least lithium (Li), and a lighting apparatus using the lamp.
2. Description of Related Art
In view of the increasing popularity of LCD projectors, there is increased demand for lighting sources that can be effectively and efficiently utilized in such devices. It is desired that such lighting sources be small, bright, and have the proper color balance. Usually, such light sources are used to back light an LCD. Light passing through the LCD is then projected onto a screen. In order to make the high-pressure mercury discharge lamp as small as possible, it is desirable to minimize the distance between electrodes of the lamp. This arrangement requires that the voltage across the electrodes be lower than the voltage across electrodes that are further apart in other lamp arrangements. Therefore the lamp must be operated at a higher current than lamps whose electrodes are further apart. The higher current requirement, in turn, requires a that a larger ballast be used for starting the lamp. Thus, an LCD projector including the lamp and its required ballast must be made relatively larger.
Japanese Laid Open Patent Application HEI 6-52830 (prior art 1) discloses a high-pressure mercury lamp utilizing an arc discharge shortening technique that does not require lowering the lamp voltage. Rather, the pressure of the filling gas is raised, which allows for higher voltage operation even though electrode spacing is reduced. The lamp of prior art 1 lights up at high-pressure mercury vapor, e.g., 10 Mpa or more during the lamp operation to provide sufficient illuminance and color rendering so as to be suitable for use in a small size projector.
In order to maintain an arc discharge, the lamp which is disclosed in Japanese Laid Open Patent Application HEI 11-297269 (prior art 2), contains a metal halide including one or more selected form a group of lithium (Li), sodium (Na), cerium (Ce), barium (Ba) and calcium (Ca). A discharge vessel of the lamp contains the metal halide of 2*10xe2x88x924 to 7*10xe2x88x922 xcexcmol/mm3. The ionizing voltage of a metal halide is 0.87 times or less than that of mercury (Hg). Such a lamp radiates more energy in the red portion of the color spectrum, so that the lamp has improved color rendering.
The inventions claimed herein, at least in one respect, feature a high-pressure mercury discharge lamp and a lighting apparatus using the lamp. The lamp and lighting apparatus are able to provide improved color rendering and color temperature without sacrificing luminous efficacy.
In one embodiment of the invention, a high-pressure mercury discharge lamp is provided. It includes a light-transmitting discharge vessel defining a discharge space and having a seal portion. Spaced apart electrodes disposed in the discharge vessel define a discharge path. A gas filling contained in the discharge vessel includes mercury, halogen and lithium (Li), whose relative spectral energy distributions are shown in FIG. 2. It is preferable that the relative spectral energies B/A be in a range of 0.15 to 0.45; wherein A represents the relative spectral energy of mercury (Hg) within the 402.5 nm to 407.5 nm wavelength range, and B represents the relative spectral energy of lithium (Li) within 667.5 nm to 672.5 nm wavelength range.
The inventions also include a lighting apparatus. The lighting apparatus includes a high-pressure mercury discharge lamp, a reflector fixing the lamp focusing the center of discharge vessel on the focal point thereof and a housing accommodating the lamp and the reflector.
These and other aspects of the invention are further described in the following drawings and detailed description of the invention.